Method of making an insulated strip conductor



Au 1, 1 6 I. w. WADE, JR.. ETAL 3,333,999

METHOD OF MAKING AN INSULATED STRIP CONDUCTOR Filed Aug. 11. 1965INVENTORS IV W. E, JR.

N AN EEBE 32 M 1 dflwg ATTORNEYS v United States Patent 3,333,999 METHODOF MAKING AN INSULATED STRIP CONDUCTOR Ivan William Wade, Jr., Muskegon,and Norman Percy Beebe, Spring Lake, Micl1., assignors to Anaconda Wireand Cable Company, a corporation of Delaware Filed Aug. 11, 1965, Ser.No. 478,952 2 Claims. (Cl. 156-3) This invention relates to electricallyinsulated strip conductor for use in manufacturing electrical coils andthe like. More particularly, it is directed to a method of manufacturingelectrically insulated strip conductors and to the strip conductors perse which are fully insulated along their side edges by integral marginaledge portions of insulating films covering the broad faces of the strip.

In the manufacture of insulated magnet strip conductors such as arecommonly used for the manufacture of electrical coils, it is essentialthat the insulating coatings which are applied to the copper strip befree from discontinuities which might cause short circuits in theirelectrical application. The most common source of these discontinuitiesin the insulating coating has been found to occur along the side edgesof the strip conductor. These side edges are the most common source offailings both because they are so difficult to coat properly withinsulating varnishes or lacquers and also because they present such arelatively sharp edge that the insulating coatings either do not adhereproperly or they become scraped off during handling, such as the windingoperation required to form electrical coils. A method often followedwith aluminum strip conductors is to insulate them with an oxidicdielectric film.

In forming the narrow strips in the fabrication of the strip conductors,the method almost universally followed is to cut narrow strip from amuch wider strip. When this wide strip is cut longitudinally intonarrower strips, the cutting operation always exposes the side edge ofthe narrower strip and leaves them rough with slivers and burrs. Thus,even if the wider strips are coated with a dielectric insulating coatingbefore the cutting operation, the flat surfaces may be adequatelyinsulated, but the side edge portions must be covered over with asuitable insulation or they would surely be the source of a shortcircuit particularly in their use of electrical coils.

It is an object of this invention to provide an electrical stripconductor which is insulated along its side edges with integral marginaledge portions of the insulating films covering the broad faces of thestrip, so that the strip conductor is completely insulated within theseinsulating films; the strip conductor is thereby insulated with aninsulating film which is continuous throughout its length and isresistant to removal by abrasion during handling.

Broadly stated, the electrically insulated strip conductor comprises astrip conductor with an electric insulating film on both flat surfacesof the strip conductor with the marginal side edges of the insulatingfilm extending outwardly beyond the side edges of the strip conductorand folded back against the side edges of the strip conductor. Therespective edges of folded back marginal edge portions of the insulatingfilm along each side edge of the strip conductor are adjoined and sealedto each other to insulate the side edges of the strip andfully insulatethe strip conductor with said dielectric insulating fihn.

The method by which these strip conductors can most advantageously bemade is first to coat the broad faces of a relatively wide metal stripwith a dielectric film and then cut the strip into a plurality ofrelatively narrow strips which are each bare of any coating at theirside edges. The side edges of the strip conductor are then etched backbetween the dielectric film on the flat surfaces to form marginal edgeportions of dielectric film 3,333,999 Patented Aug. 1, 1967 whichproject beyond the etched 'back side edges of the strip conductor. Theprojecting marginal edges of the dielectric film are then folded againstthe side edges of the strip conductor and heat sealed together toinsulate the side edges of the strip conductor and fully insulate thestrip conductor with said dielectric film.

Unlike strip conductors heretofore made, the strip conductor of theinvention is fully insulated both at its broad faces and at its sideedges by integral portions of dielectric film which are joined along theside edges. Because of the unitary and continuous coating of insulationfrom the broad faces around the sharp edges and against the side edgesof the strip conductor, the problem of inadequate insulation at theedges is eliminated because the side edges are not insulated in asecondary operation by applying a separate dielectric insulation to theedges. Moreover, because the insulation folded and sealed along the sideedges was formerly applied as a uniform thickness coating to the broadfaces of the strip, upon etching back, the side edges the marginal edgeportions which extend beyond the side edges of the strip conductor areof the same uniform thickness as on the film on the broad faces of thestrip conductor since these extended marginal edge portions formerlycovered a broad face of the sheet. Thus, upon sealing along the sideedges of the strip a dielectric insulation of the same strength isprovided along the side edges as well and a uniformly insulated stripconductor is realized.

A preferred embodiment of the invention is described below withreference to the drawing wherein:

FIG. 1 is a schematic of the steps in the method of forming theelectrically insulated strip conductors;

FIG. 2 is a fragmentary section of the strip conductor takensubstantially along lines 2-2 of FIG. 1;

FIG. 3 is a fragmentary section of the strip taken substantially alonglines 3-3 of FIG. 1;

FIG. 4 is a fragmentary section of a side edge of the strip duringfolding of the insulating film about the side edges taken substantiallyalong the lines 4-4 of FIG. 1; and

FIG. 5 is a fragmentary section of a side of the strip upon completionof the folding of the insulating film about the side edges takensubstantially along the lines 55 of FIG. 1.

As shown in FIG. 1, a coil 10 comprises a multiplicity of turns of flatmetal strip, usually aluminum or copper of say .003 inch thickness. Thecoil 10 is substantially wider than the desired magnet strip conductorwidth and is first fed to a coating station 11 where a liquid organicdielectric coating composition, for example a polyvinyl acetal, such asa polyvinylformal, or a silicone insulating enamel is applied to bothbroad faces of the wide flat metal strip. This coating can be appliedbyspray, roller, gravure, dip and the like, provided-a layer of suchcomposition of uniform thickness is transferred to the broad faces ofthe advancing strip. Upon emerging from the coating apparatus, thecoating composition is dried to a hardened condition.

The wide coated strip 12 is then directed through a slitting station 13where a conventional continuous cutting apparatus is located forslitting the advancing wide strip longitudinally into a plurality ofnarrow strips. As shown in FIG. 2 a narrow width strip 14 is formed byslitting which has a uniform thickness dielectric film 15 and 16 on eachbroad face, but the side edges 17 of the strip are bare of insulation asthe insulating films are coextensive with the side, edges of the strip.

The narrow strips exiting from the cutting apparatus are preferably thenwound into a roll 18 while a thin plastic sheet is simultaneously fedwith the strip conductor so that the roll is interleaved with this thinplastic sheet between successive turns. Polyethylene sheets have beenused with success for this operation. Also the rolls can be interleavedwith another sealant such as a heavy liq i like kerosene.

The roll 18 is then transferred to an etching station 19 where the sideedges 17 are etched back to remove a portion of the strip conductoralong the side edges and leave a void 20 between the insulating filmsand define new side edges 21 along the strip of reduced width as shownin FIG. 3. Marginal edge portions 22 and 23 of the insulating filmextend laterally out beyond the side edges 21 of the strip conductor onboth sides, and the side edges are still free from insulation. Theetching bath can contain any of the conventional etching reagents suchas a nitric acid or hydrochloric acid solution for aluminum or a ferricchloride solution for copper. Alternatively, the etching may be carriedout in an electrolyte by making the roll the anode.

The plastic sheet or other sealant which is interleaved between theturns of the roll serves as a barrier to the etching solutionpenetrating between the turns of the roll where it might react with theinsulating film and bond the turns together. Depending upon theinsulating film used and method of etching selected, it may not benecessary to have any form of sealant between turns.

After etching, the etched strip is removed from the roll and. passed toa heat forming station 24 where heated forming rolls 25 are located onboth sides of the strip being advanced therethrough. As shown in FIGS. 4and 5, the rolls are configured to receive the edges of the strip andprogressively fold the extended integral marginal edge portions 22 and23 of the dielectric insulating films 15 and 16 around the edges anddown against the side edges 21 of the strip until the end edges 26 and27 of adjacent marginal side edge portions meet and are heat sealedtogether longitudinally along the respective side edges thereof as shownin FIG. 5. By this construction the strip conductor is fully insulatedby a uniform thickness of dielectric insulation. The side edges areinsulated by integral marginal portions of the insulating films whichinsulate the broad faces of the strip conductor and the need to apply asecondary and separate side edge insulation is eliminated. It has beenfound that a strip conductor with the side edges coextensive with theinsulation coating on the broad faces as shown in FIG. 2 has adielectric strength which essentially measures zero. Once the side edgehas been etched back as shown in FIG. 2 the dielectric strength variesfrom to 100 v. After folding and heat sealing the marginal edge portionsof the insulating film as shown in FIG. 5, the dielectric strengthincreases to 200-500 v.

When the strip is finally formed it is Wound into a roll of insulatedstrip conductor which is excellently suited for rewinding into amultilayer coil with the organic electric insulating film disposedwithin successive layers of the coil, and then suitable leads areattached,

We claim:

1. A method of making an electrically insulated strip conductorcomprising:

(a) coating the broad faces of a relatively wide strip conductor with adielectric film,

(b) cutting the strip conductor into a plurality of relatively narrowstrip conductors which are each bare of any coating at their side edges,

(c) etching at least one of the side edges of the strip conductor backbetween the dielectric film on the flat surfaces to form integralmarginal edge portions of dielectric film which project beyond theetched back side edges of the strip conductor,

((1) folding the projecting marginal edges of the dielectric film aroundthe sharp edges of the conductor against the etched side edges of thestrip conductor in adjoining contact with the adjacent marginal sideedge portion on the opposite broad face of the strip conductor, and

(e) heat sealing the adjoining side edges together to fully insulate theedge of the strip conductor With said dielectric film.

2. A method of making an electrically insulated strip conductorcomprising:

(a) coating the broad faces of a relatively wide strip conductor with auniform thickness film of dielectric coating composition,

(b) cutting the wide strip conductor longitudinally into a plurality ofrelatively narrow strip conductors characterized by said films on eachbroad face being coextensive with the side edges of the narrow stripconductor, which side edges are each bare of any dielectric coating,

(c) winding the narrow strip conductor into a roll,

(d) etching the side edges of the strip conductor in roll form backbetween the layers of dielectric to define integral marginal edgeportions of said dielectric films projecting beyond the etched back sideedges of the strip conductor,

(e) unwinding the strip conductor from the roll,

(f) folding the integral marginal edge portions around the sharp edgesof the strip conductor against the respective etched side edges of thestrip conductor in adjoining contact with the edges of adjacent marginalside edge portion of layers on opposite faces of the strip conductor,and

(g) heat sealing the adjoining edges together longitudinally along therespective side edges of the strip conductor to fully insulate the stripconductor within the dielectric composition.

References Cited UNITED STATES PATENTS 2,393,486 1/1946 Storch.2,728,036 12/1955 Steiner 317260 FOREIGN PATENTS 699,274 11/1953 GreatBritain.

LEWIS H. MYERS, Primary Examiner.

E. GOLDBERG, Assistant Examiner.

1. A METHOD OF MAKING AN ELECTRICALLY INSULATED STRIP CONDUCTORCOMPRISING: (A) COATING THE BROAD FACES OF A RELATIVELY WIDE STRIPCONDUCTOR WITH A DIELECTRIC FILM, (B) CUTTING THE STRIP CONDUCTOR INTO APLURALITY OF RELATIVELY NARROW STRIP CONDUCTOR WHICH ARE EACH BARE OFANY COATING AT THEIR SIDE EDGES, (C) ETCHING AT LEAST ONE OF THE SIDEEDGES OF THE STRIP CONDUCTOR BACK BETWEEN THE DIELECTRIC FILM ON THEFLAT SURFACES TO FORM INTEGRAL MARGINAL EDGE PORTIONS OF DIELECTRIC FILMWHICH PROJECT BEYOND THE ETCHED BACK SIDE EDGES OF THE STRIP CONDUCTOR,(D) FOLDING THE PROJECTING MARGINAL EDGES OF THE DIELECTRIC FILM AROUNDTHE SHARP EDGES OF THE CONDUCTOR AGAINST THE ETCHED SIDE EDGES OF THESTRIP CONDUCTOR IN ADJOINING CONTACT WITH THE ADJACENT MARGINAL SIDEEDGE PORTION ON THE OPPOSITE BROAD FACE OF THE STRIP CONDUCTOR, AND (E)HEAT SEALING THE ADJOINING SIDE EDGES TOGETHER TO FULLY INSULATE THEEDGE OF THE STRIP CONDUCTOR WITH SAID DIELECTRIC FILM.